Auger Electron Angular Distributions from Surfaces: Direct Comparison with Isoenergetic Photoelectrons

Abstract

Angular distribution patterns of Auger electrons and of photoelectrons from a Cu (001) surface were measured at the same electron kinetic energy. These measurements reveal that the low kinetic energy angular distributions for Cu Auger electrons and Cu 3p(3/2) photoelectrons differ substantially. This direct comparison between the photoelectron and Auger electron angular distributions demonstrates that, in some circumstances, the Auger process produces a complicated source wave whose nature must be explored before Auger angular distributions can be used for surface structure analysis.

X-ray photoelectron diffraction and Auger electron diffraction fromTiO2(100)

“…Interatomic directions in the crystal can be determined from these forward scattering spots, since at these kinetic energies the greatest intensity is found in the forward scattering direction when the emitter, scatterer, and detector are aligned. 1,2, 19 The simplest way to do this is to compare the experimental results with the plots shown in Fig. 3.…”

“…Early experiments assumed that Auger electrons could be treated as s waves with an isotropic angular distribution, 16,17 but more recent work has shown that it is important to take the angular momentum of the outgoing Auger electron wave into account. 18,19 To take the Auger electron angular momentum into account, we have performed calculations for electrons with different values of the angular momentum quantum number l. In Fig. 8 Fig.…”

“…16,17 However, more recent results have shown that the final state of the Auger electron should be taken into account if the best agreement between theory and experiment is to be obtained. 18,19 This requirement to take the source wave character into account becomes even more important at lower kinetic energies, i.e., Ͻ100 eV, as has been demonstrated for metal surfaces such as Cu͑001͒, Al͑001͒, and Pt͑111͒. 19 The analysis of AED is further complicated by the nature of the multielectron Auger process, which involves coupling of the electron initial states, giving various possible final state angular momentum distributions.…”

“…18,19 This requirement to take the source wave character into account becomes even more important at lower kinetic energies, i.e., Ͻ100 eV, as has been demonstrated for metal surfaces such as Cu͑001͒, Al͑001͒, and Pt͑111͒. 19 The analysis of AED is further complicated by the nature of the multielectron Auger process, which involves coupling of the electron initial states, giving various possible final state angular momentum distributions. 20 Theoretical calculations of the diffraction patterns are needed to fully utilize these Auger data.…”

Photoelectron Diffraction and Synchrotron Radiation

“…different final state angular momenta, at constant energy, and should therefore be very important to further our understanding of this interplay. One such study has recently been published by Terminello and Barton [26], comparing the patterns of Cu Μ2,3Μ4,5Μ4,5 and Cu 3p emission from Cu(001), both at 60 eV. Their results indicate that the source wave effects are very important at this energy.…”